Gaseous fuel control system and apparatus for furnaces



1967 E. H. MANNY 3,346,249

GASEOUS FUEL CONTROL SYSTEM AND APPARATUS FOR FURNACES Original FiledDec. 1, 1960 Tuyeres Vent Remote Operated Shut Off FuelSu l PressureReducing we Station Blast Air &

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mmw s\ ERVIIN H. MANNY INVENTOR PATENT ATTORNEY United States Patent3,346,249 GASEOUS FUEL CONTROL SYSTEM AND APPARATUS FOR FURNACES ErwinH. Manny, Cranford, N.J., assignor to Esso Research and EngineeringCompany, a corporation of Delaware Original application Dec. 1, 1960,Ser. No. 73,000, now Patent No. 3,210,181, dated Oct. 5, 1965. Dividedand this application Dec. 17, 1964, Ser. No. 418,993

3 Claims. (Cl. 26629) ABSTRACT OF THE DISCLOSURE An apparatus forcontrolling the injection of gaseous fuels and blast air into a blastfurnace, which apparatus assures positive gas flow to the blast furnaceat all times in step with blast air temperature and volume bymaintaining a positive pressure differential of the gas over the blastair.

The present invention relates to a fluid control apparatus and methodfor furnaces. In particular, the invention concerns an apparatus andprocess for controlling the injection of gaseous fuels and blast gasesinto a furnace, and more particularly, the controlling of the injectionof natural and refinery gases and heated blast air into a blast furnace.This application is a divisional application of application Serial No.73,000, filed December 1, 1960, now Patent No. 3,210,181, which is acontinuationin-part of application Serial No. 38,852, filed June 27,1960, now Patent No. 3,228,764.

In the operation of a conventional blast furnace, the furnace is chargedwith iron ore (iron oxides), flux materials (limestone) and carbonaceousmaterials (coke). This mixture is then heated to drive off carbondioxide and water, and as the ore descends downward through the stack,it is reduced to iron by reducing gas moving in a countercurrentdirection. The reduced iron is then melted in the lower bosh portion ofthe furnace, and the liquid metal withdrawn through the iron notch atthe hearth. A blast furnace thus requires a source of reducing gas inthe upper part of the stack to reduce the ore and, a high temperature inthe lower part of the stack (bosh section) sufficient to melt andliquify the reduced ore. Both requirements are generally provided for byintroducing a heated air or an oxygen-enriched air mixture through aseries of circumferential tuyeres located near the bottom of thefurnace. The air blast combusts with the coke to furnish the necessaryhigh temperature to melt the iron (2,500 to 3,000 P.) and a reducing gas(carbon monoxide) to reduce the ore further up the stack.

It is known in the art that hydrocarbon fuels may be used as a partialreplacement for coke in the blast furnace. Suitable fuel for thispurpose would include any liquid, liquefiable, gaseous or emulsifiablehydrocarbon fuel product. Gaseous hydrocarbon fuels suitable for use inblast furnaces and with the present control system include natural gas,acetylene, blast furnace lay-product gas, water gas, carbureted watergas, coal gas, coke oven gas, hydrogen, oil gas, reformed gas, lightpetroleum gases, producer gas, petroleum refinery gases, and the like.Suitable gaseous fuels are more fully set forth in the ChemicalEngineers Handbook, 3rd edition, pp. 1575 1596. These gaseous fuels aremost suitably utilized by injecting them in conjunction with the heatedblast air either through the tuyeres or near the tuyeres into the loweror bosh portion of the blast furnace, cupola, open heart-h furnace, orother furnace to produce high temperatures and suitable reducing gases.

3,346,249 Patented Oct. 10, 1967 The problems associated with theinjection of gaseous fuels and the efficient operation of a blastfurnace involve the close control of certain blast furnace variables. Itis important that the injection of the gaseous fuel be closelycontrolled so that the injection of excessive fuel at the blast airtemperature employed will not upset the furnace operation. Hightemperatures will allow the partly reduced ore in the upper part of theshaft to become pasty, slump together, and reduce or cut off the passageof the blast and reducing gases, thus choking the furnace, while evenhigher temperatures may destroy the furnace by causing the lining toslag. Low temperatures also must be avoided in order not to freeze thefurnace, thereby causing uncontrolled cooling with consequent failure ofthe material to move down the stack and possible destruction of thefurnace lining. The correct operation of the furnace is usually theresponsibility of the furnaceman, who by visual observations of thefurnace operations through the peephole in each individual tuyere, andthe data available maintains the furnace at the optimum conditions,detecting and correcting operating difficulties.

Control of operating conditions has in the past been usually affected bycontrolling the volume, temperature, moisture and other factors of theblast air. The injection of gaseous fuels with the blast air createsnovel, additional and critical problems in the proper control of fuelflow, air blast flow, temperatures, the detection of operatingdifficulties, safety hazards and the like. Thus, for example, blast airand fuel flow must be maintained in certain critical operatingproportions to ensure proper operating temperatures. The cutoff orreduction in flow of the fuel or blast must be accompanied by a suitablereduction or cutoff of the other component, otherwise operatingtemperatures may not be suitable for proper furnace operation. Inaddition, the plugging of individual tuyeres by coke, slag, iron orcarbonaceous material, and the burning of gaseous fuel in the individualtuyere, must be detected and corrected promptly for efficient operation.Another problem in the use of gaseous fuels is that the blast airtemperature must be higher to achieve maximum coke reduction thanconventional blast air temperature. Preferably the air blast temperatureshould be at least 1000 F., with a range of 1400 F. to 2400 F., thepresent maximum practical, especially preferred with gaseous fuels. Thisis necessary since the initial cracking reaction of the relatively coldgaseous fuel with the air blast produces less heat then that producedwith coke, the total heat quantity of which varies according to the fuelused. In order to reduce any absorption of heat from the bosh section athigh gaseous fuel injection rates, the temperatures of the air blastmust be increased. To avoid initial lower temperature effects in thefurnace, the temperature of the blast air must preferably then be keptabove a certain predetermined temperature level to achieve maximumreduction in coke consumption. Thus, blast air temperature and fuel flowmust be closely correlated for efficient operation. The approximatesteady uniform injection and distribution of gas at all the tuyeres isanother requirement of proper fuel injection to ensure good blastfurnace operation. Of course, the handling of combustible gases alsorequires that certain safety requirements be observed so that fuel flowis not uncontrolled. These and other problems :as sociated with the useof gaseous fuel render the conventional operation of furnaces entirelyby the judgment of the furnaceman, with limited observation and data,quite inefficient and subject to gross errors with resulting disaster tofurnace and operations and to the furnace itself. A control systemapplicable to gaseous fuels is proposed which ensures satisfactoryoperation under safe conditions. In particular, the gaseous controlsystem incorporates control means to assure positive fuel flow to the 3blast furnace at all times in step with blast air flow and temperature.

It is therefore an object of the present invention to provide a methodand apparatus for the proper detection and control of certain criticalvariables in the operation of furnaces utilizing a gaseous fuel-airinjection system. Other objects are the proper control of gaseous fuelflow and blast air fiow in blast furnaces, individual tuyeres, themaintenance of gaseous fuel flow with certain minimum air blasttemperature, and the maintenance of positive gas flow to the blastfurnace. These and other objects as well as the nature and scope of theinstant invention will be more apparent from the following drawings anddescription.

The present invention will be more fully understood by reference to theaccompanying drawings wherein:

FIGURE 1 is a diagrammatical representation of a gas piping and controlsystem for blast furnaces.

FIGURE 2 is a diagrammatical representation of the inventive gaseousfuel-air blast control system for a blast furnace.

Referring now to FIGURE 1 in more detail, there is shown a system forthe introduction of gas into a blast furnace wherein the gas, such asnatural or refinery gas supplied at a high pressure, is reduced tobetween 25 to 100 p.-s.i.g. and preferably to about 60 p.s.i. at apressure reducing station. Valve means for a remotely operated shutoifof the gas supply are built into the pressure reducing valve to providesafe and positive isolation of the fuel supply from the blast furnaceduring shutdown. Meter means are also provided to provide a measure oftotal fuel flow. The relatively low pressure gas is then fed through amain supply line to a shutoif and vent cock arrangement, a meter with abypass, and a fuel controller 40 and then to a gas ring manifold 16,which circumferentially surrounds the blast furnace, preferably aboutthe bush section. Radially inwardly extending from the gas ring manifoldare individual gas injection pipes into or near each individual tuyereof the blast furnace. T o obtain uniform and steady distribution of thegaseous fuel contacting the ore, coke, and flux stock in the furnace,uniform amounts of gas must be injected at each individual tuyere. Sincethe blast furnace usually operates at pressures between 20 and 30p.s.i.g., the fuel supply system must be properly designed to deliversulficient gaseous fuel within the 30 to 40 p.s.i. pressure drop. Thegas ring manifold must be sized for little or no pressure drop betweenthe gas inlet and the last tuyere to ensure uniform distribution ofgases in the furnace using the same external tuyere orifices. Of course,the blast air injected into the blast furnace is always at a higherpressure than the blast furnace pressure, so that by maintaining thefuel at a positive differential above the blast air the fuel pressurewill additionally be above the furnace pressure.

Although the control system described herein contemplates control of thetotal flow of air blast and gaseous fuel, gas-air proportioning may alsobe accomplished at each individual tuyere at increased cost. Theapproximate maximum quantity of natural or refinery gas used by blastfurnaces of different capacities and the required pipe sizes of thesupply line are shown in Table I.

TABLE I Blast Furnace Natural Gas Approximate Production, TonsConsumption, Pipe Size, Hot Metal/D. 1,000 s.c.f./D. Inches Referringnow to FIGURE 2, there is shown a preferred fuel-air injection controlsystem with a sectional view of an individual tuyere, wherein preheatedatmospheric air or oxygen enriched air at about 50,000 to 100,000 cu.ft./min. at a higher then atmospheric pressure, for example, 25p.s.i.g., is forced through a bustle pipe 10, which circumferentiallysurrounds the blast furnace. An individual tuyere blowpipe 11communicates through an elbow and a gooseneck with the bustle pipe andprovides means whereby the blast air is admitted into the blast furnace.Within the individual tuyere chamber or blowpipe is located a fuelinjection pipe 70, the outside end of which extends through the elbowand has a manual shutoff valve. The fuel injection pipe could, ifdesired, be located outside of the tuyere, but adjacent to the tuyere toensure proper combustion conditions.

The fuel injection pipe can be a straight tube injection pipe as shown,or, if desired, a fluid shrouded tube, for example, a shrouded aircooled tube. The latter nozzle would be suitable and preferred since theheated blast gas (about 2,000 P.) and furnace heat of the raceway (about3,400" F.) are sufficient to cause excessive carbonization and thermalcracking of the gaseous fuel, along with the hazard of auto-ignition ofthe gas-air mixture. Thus, the latter nozzle comprising an annular-typetube or duct-type conduit or its equivalent surrounding the fuelinjection pipe would be desired. By passing relatively cool air throughthe surrounding tube, the gaseous fuel being injectml would be protectedfrom excessive heat effects and carbonization and auto-ignition of themixture inhibited. The protecting air flow and pressure would be suchthat on stoppage of the fuel flow, the air effect on the furnacetemperature conditions would be negligible. A suitable fluid shroudwould be air having a temperature of from 60l50 F. at a pressure of from2l0 pounds per square inch.

The outside end of the injection pipe is connected to a braidedcorrugated flexible metal tubing 14, which communicates in turn with anindividual tuyere gas supply line 15 which is further connected to thegas ring manifold 16, where the gaseous fuel is under suitable positivepressure at least 1 psi above the pressure of the blast air pressure.The ring manifold is supplied gaseous fuel by a main gas supply line 19at pressures ranging between 25 and 75 p.s.i.g. and preferably about 60p.s.i.g. The corrugated tubing 14 permits quick disconnection of thefuel injection pipe and convenient access to the individual tuyere.Located below the injection pipe in the elbow is the conventionaleyesight or peephole 18, whereby the furnace conditions are observed bythe furnaceman. In the fuel supply line is located a differentialpressure gauge 21, positioned across an orifice 17, whereby anyobstruction in the individual gas injection pipe of the tuyere resultingin an unequal fuel distribution with other individual tuyeres will bepromptly detected by a change in pressure across the orifree, and thefurnaceman alerted by an alarm, e.g. signal light, that the injectionpipe is plugged or partially clogged and must be cleaned to restorenormal flow. Although steam or air purge means to purge the individualfuel injection pipes on shutdown of the fuel supply are not shown, theymay be incorporated as described in the parent application whenexcessive carbonization of the gaseous fuel requires it.

The gaseous fuel supply to the ring manifold is controlled by a fuelflow recorder-controller 40, the blast air to the bustle pipe by a blastair controller 50 and the pressure difference between the blast air andgaseous fuel maintained by a differential pressure controller 30, all ofwhich controllers communicate and interlock with a control relay asshown. The controllers are any suitable flow control means capable ofmanual or automatic operation from a control relay system. Suitablecontrollers would thus include diaphragm, power cylinder, or electricmotor operated steam, air, or liquid flow controllers or flowrecorder-controllers of the globe or V port-type which are well known inthe art. The preferred controllers are a standard globe valve flowcontrol apparatus operated by pneumatic means. Suitable controllersinclude those set forth in the ASME Mechanical Catalogue of 1960,particularly FIGURE 13, page 43; and in the December 1949 issue ofPower, pages 71-106 and in particular FIGURE 3 of page 101. Control ofthe blast air can also be accomplished in the conventional manner byregulating the speed of the air blower or by venting of the air blast tothe atmosphere. The fuel flow controller can be modified slightly toprovide for visual or graphic recording means for observing the quantityof fuel being used or used during a certain period of time. The blastair and fuel flow are capable of manual control by the furnaceman or canbe automatically controlled by the control relay. The control relay canbe any suitable mechanical, hydraulic, electronic and the like, relaysystem which will interlock with the controller used so as to performthe functions intended. These types of control relay systems like thecontrollers are well known to those skilled in the art. Suitable controlrelays would include pneumatic relays such as the Standatrol type, aproportioning diaphragm pneumatically operated, relay manufactured bythe Bailey Meter Company, and electronic relays such as the magnet bartype. Suitable and preferred relays are further listed in the ASMEMechanical Catalogue of 1960 on page 43, FIGURE (pneumatic type) and inthe December 1949 issue of Power on page 88, FIGURE 5 (pneumatic type)and page 104, FIGURE 2 (magnet bar type). With the gaseous fuel controlsystem shown, the use of a compressed air-operated control relay wouldbe most economical and preferred.

Communicating with the differential pressure controller and located inthe main fuel supply line is a valve control mechanism 80 which operatesto open and close simultaneously shutoff valves 81 and 82 and to openvalve 83 to vent or discharge the gaseous fuel to the atmosphere whenthe shutoff valves are closed. This shutoff and vent valve arrangementreduces safety hazards, for example, gas leaking and the like, attendantwith the use of the gaseous fuels by providing a positive shutoff andsafe venting of the gas at a distance from the blast furnace. The valves81, 82 and 83 are interconnected to operate in sequence with oneanother. The valve control mechanism may be a valve-driven mechanism asshown operating by impulses received from the differential pressurecontroller or the fuel controller. Suitable valve mechanisms would thusinclude mechanically, electrically, and hydraulically operated solenoidsand other means more known to the art.

The differential pressure controller is interlocked with the controlrelay and the fuel controller. The pressure controller operates toassure that a positive gas flow to the blast furnace will be maintainedat all times. The pressure controller continuously monitors the pressureof the blast air in the bustle pipe and controls the gaseous fuel in thering manifold as shown to a predetermined differential pressure, usuallybetween 1 and 50 p.s.i.g., for example, 2 p.s.i., of the gaseous fuelover the blast air. Economic reasons would indicate a preference for arather low pressure differential. The differential pressure controllerthus communicates with the fuel controller, and provides for thestoppage of fuel flow when a positive predetermined pressuredifferential cannot be maintained over the blast air. This pressurecontroller thus operates to override the fuel controller when the presetfuel-air ratio of the control relay attempts to throttle gaseous fuelbelow the preset positive pressure differential. This action assuresthat blast air will not backfiow through the gaseous piping system andcreate hazardous air-gas explosive mixtures. When the pressurecontroller actuates to close the fuel controller or if the controlrelay, upon failure or reduction of the blast air volume or temperature,closes the fuel controller, the valve drive mechanism is also actuatedand the shutoff valves close and the vent valve opens. The differentialpressure controller only functions when positive gasflow to the furnaceis threatened.

In the automatic operation, the blast air controller and the fuelcontroller are interlocked through the control relay so that the fuelcontroller will close (fail-safe) on low blast air pressure or flow asindicated by low pressure or flow in the bustle pipe. In addition, thefuel controller will close at a predetermined minimum blast temperaturelevel or, if this is desired, to be left to the judgment of thefurnaceman, appropriate visual or aural signals can call his attentionto lower blast air tempertures. The interlockin-g operation of the fueland blast air controller will thus prevent safety hazards fromoccurring, and prevent the furnace from freezing or otherwisemalfunctioning. The control relay by measuring the flow rates andpressures can also maintain a proper preselected fuel/air ratio. Whenblast air is modulated in volume, the fuel flow will be automaticallyreduced or increased in flow to maintain a proper fuel/air blast ratio.Any attempt to modulate fuel flow below the predetermined presuredifferential will be prevented by the differential pressure controller.When blast air flow is reduced or shut off, such as in the tappingcycle, the fuel flow recorder-controller will automatically shrut offthe fuel supply. Manual means of overriding this control can be providedto permit the flow of gaseous fuel at reduced blast air flow. Manualcontrol through the control relay also allows the furnacemen, uponresumption of operations, to delay the injection of fuel to the furnaceuntil furnace conditions are satisfactory.

The fuel controller permits the desired quantity of fuel to flowprovided sufficient differential exists between the gas and the blastair in the system. When no differential exists as in the startupoperation, means are provided to override the differential pressurecontroller to permit the fuel controller to operate. Thus, in essence, acontrol system is provided whereby a preselected air-fuel ratio in stepwith furnace conditions is provided. Upon failure of the blast air,reduction of the blast air temperature or volume below a preselectedminimum, e.g., 1800 F., or failure or reduction in gaseous fuel supply,the fuel controller, through impulses received by the control relay,stops the flow of fuel and the valve mechanism is simultaneouslyactuated by closing the shutoff valves and opening the vent valve. Inthis operation, manual controls are also provided to allow thefurnaceman to alter conditions to suit furnace operation. The fuel flowis also continuously monitored by the differential pressure recorder toensure a positive flow of gaseous fuel to the furnace, so that thedifferential pressure controller will override the fuel controller andstop gas flow only when the pressure is reduced below the safety margin.

An individual fuel safety controller is located in the fuel supply linebetween the gas ring manifold and the individual tuyere and interlockedby an interlock relay shown to a thermocouple 61 and a pitot tube 62 ineach individual tuyere. The interlock relay as shown is a standard relaycontrol and can be any suitable mechanical, hydraulic, electronic meanscapable of performing the functions described. Suitable interlock relayswould include those relays as described for the control relay since thefunction and structure of the interlock relay is the same as the controlrelay except that interlock relay operates on individual tuyere linesrather than on the total gaseous or blast manifold flow. This interlockrelay is designed to shut off the fuel supply to the individual tuyereand signal the fumacemen upon the stoppage of blast air or burningwithin the tuyere or blowpipe. The pitot tube, orifice plate, or otherair flow measuring device installed in each tuyere operates to indicatethe blast air flow, and that the tuyere is not plugged or partiallyclogged. When the tuyere becomes plugged by coke, slag, molten iron, andthe ll ke, the drop in differential pressure actuates the relay to shutoff the individual fuel supply to that tuyere. In the absence of suchcontrol, there will be no simple way of detecting the stoppage of airflow; thus combustible gas will continue to flow and fill the tuyere,creating a safety hazard. The pitot tube controls detect thisoccurrence, stop the fuel flow and notify the furnacemen. In addition,the blast air flow in the tuyere as monitored by the pitot tube throughthe interlock relay maintains the correct individual tuyere fuel/airrelationship. This is particularly important since the air flow in eachindividual tuyere varies considerably depending upon the internalfurnace conditions such as channelling and the like. The location of athermal sensing means, such as a switch or thermocouple, in eachindividual tuyere prevents gas from burning in the tuyere undetected.The high temperature of the air blast and the raceway makes individualfires in the tuyere with subsequent destruction of the slender injectionpipe a real danger. Thus, upon an increase in temperature in the tuyeredetected by the thermocouple in the blast pipe, the individual fuelsupply is automatically shut off through the interlock relay, by thefuel safety controller, and the furnacemans attention is called to thesituation by a signal alarm system.

The inventive control system described solves many of the novel andintricate problems in the utilization of gaseous fuels in furnaces. Inparticular, the inventive system assures positive gas flow to the blastfurnace at all times in step with blast air temperature and volume andreduces the hazards of combustible gas-air mixtures.

What is claimed is:

1. An apparatus for the control of the gaseous fuelblast air flow in afurnace provided with a bustle pipe and a tuyere located on the side ofthe furnace so as to permit heated blast gases to flow through thebustle pipe and into the tuyere for injection into the furnace, whichapparatus comprises in combination: a fuel source; a gas ring manifoldfed by the fuel source; a fuel injection pipe communicating with thering manifold whereby gaseous fuel is allowed to flow from the ringmanifold into said injection pipe; means to measure the blast airtemperature; a blast air flow recorder-controller; a fuel flowrecorder-controller; a differential pressure recorder-controller, whichcontroller monitors the pressure differential between the air blast ofthe bustle pipe and the fuel in the ring manifold; a control relay whichis interlocked with the blast air, fuel flow and differential pressurerecorder-controllers and the temperature measuring means; means tomonitor the recordings of the recorder-controllers and temperaturemeasuring means to the control relay; means whereby said control relayactuates the fuel controller and stops fuel flow when one of thefollowing functions occurs: (a) upon reduction in the blast airtemperature to any predetermined value; (b) upon reduction of the blastair flow to any predetermined value; and (c) upon reduction of the gaspressure in the ring manifold to any predetermined positive pressuredifferential from that of the blast air in the bustle pipe.

2. An apparatus as defined in claim 1 wherein said fuel injection pipeis located within the tuyere.

3. An apparatus as defined by claim 1 wherein said apparatus containsadditionally a valve control mechanism interlocked with said controlrelay through the differential pressure recorder controller and meansfor transferring signals from the differential pressurerecorder-controller to the valve control mechanism, whereby said valvemechanism upon closing of the fuel controller actuates shutoff and ventcocks in the fuel supply line to provide positive shutoff of the gassupply and vents gas between the blast furnace and the valve mechanismto the atmosphere.

References Cited UNITED STATES PATENTS 1,620,240 3/1927 Smoot 158 1192,072,384 3/1937 Schmidt 137 91x 2,087,842 7/1937 Gerwig 266-412,388,669 11/1945 Baker l3788X 2,605,180 7/1952 Totzek 266-30X 2,719,0839/1955 Pomykala -42 2,879,056 3/1959 Wagner 26629 2,916,022 12/1959Arant.

2,962,094 11/1960 Wallace 158 42.2X 2,980,416 4/1961 'Strassburger 266303,116,143 12/1963 Reichl 266-41X JOHN F. CAMPBELL, Primary Examiner.

R. F. DROPKIN, Assistant Examiner.

1. AN APPARATUS FOR THE CONTROL OF THE GASEOUS FUELBLAST AIR FLOW IN AFURNACE PROVIDED WITH A BUSTLE PIPE AND A TUYERE LOCATED ON THE SIDE OFTHE FURNACE SO AS TO PERMIT HEATED BLAST GASES TO FLOW THROUGH THEBUSTLE PIPE AND INTO THE TUYERE FOR INJECTION INTO THE FURNACE, WHICHAPPARATUS COMPRISES IN COMBINATION: A FUEL SOURCE; A GAS RING MANIFOLDFED BY THE FUEL SOURCE; FUEL INJECTION PIPE COMMUNICATING WITH THE RINGMANIFOLD WHEREBY WHEREBY GASEOUS FUEL IS ALLOWED TO FLOW FROM THE RINGMANIFOLD INTO SAID INJECTION PIPE; MEANS TO MEASURE THE BLAST AIRTEMPERATURE; A BLAST AIR FLOW RECORDER-CONTROLLER; A FUELRECORDER-CONTROLLER; A DIFFERENTIAL PRESSURE RECORDER-CONTROLLER, WHICHCONTROLLER MONITORS THE PRESSURE DIFFERENTIAL BETWEEN THE AIR BLAST OFTHE BUSTLE PIPE AND THE FUEL IN THE RING MANIFOLD; A CONTROL RELAY WHICHIS INTERLOCKED WITH THE BLAST AIR, FUEL FLOW AND DIFFERENTIAL PRESSURERECORDER-CONTROLLERS AND THE TEMEPRATURE MEASURING MEANS; MEANS TOMONITOR THE RECORDINGS OF THE RECORDER-CONTROLLERS AND TEMPERATUREMEASURING MEANS TO THE CONTROL RELAY; MEANS WHEREBY SAID CONTROL RELAYACTUATES THE FUEL CONTROLLER AND STOPS FUEL FLOW WHEN ONE OF THEFOLLOWING FUNCTIONS OCCURS; (A) UPON REDUCTION IN THE BLAST AIRTEMPERATURE TO ANY PREDETERMINED VALUE; (B) UPON REDUCTION OF THE BLASTAIR FLOW TO ANY PREDETERMINED VALUE; AND (C) UPON REDUCTION OF THE GASPRESSURE IN THE RING MANIFOLD TO ANY PREDETERMINED POSITIVE PRESSUREDIFFERENTIAL FROM THAT OF THE BLAST AIR IN THE BUSTLE PIPE.